It is a recurring requirement for space missions to provide means by which propellant levels can be gauged and controlled throughout the operational lifetime of a spacecraft. Conventional methods for propellant gauging include a dead reckoning method, and a thermal propellant gauging technique (TPGT). In the dead reckoning method, the current propellant level is estimated by subtracting an estimated mass of propellant burnt during all thruster firings since the mission began, from the initial level of propellant. This method and becomes increasingly inaccurate towards the end-of-life due to accumulated errors. In the TPGT method, the thermal response of the propellant tank to heating is measured and compared to simulation results for different propellant levels. A combination of dead reckoning and TPGT can also be used to estimate the remaining propellant level. However, these methods do not always satisfy the requirement for gauging accuracy throughout the on-orbit lifetime, which is typically ±10% of remaining propellant.
The invention is made in this context.